US2455984A

US2455984A - Hydraulic pressure intensifier unit

Info

Publication number: US2455984A
Application number: US573997A
Authority: US
Inventors: Gordon R Elliott
Original assignee: EDWARD U DEMMER; IRVING A PUCHNER
Current assignee: EDWARD U DEMMER; IRVING A PUCHNER
Priority date: 1945-01-22
Filing date: 1945-01-22
Publication date: 1948-12-14
Anticipated expiration: 1965-12-14

Description

Dec. 14, 1948'. y G; R. ELLIOTT 2,455,984

HYDRAULIC PRESSURE INTENSIFIER UNT Filed Jan. 22, 1945 5 Sheets-Sheet l y "WQ/maw Dec. 14, 1948.A 5.` R. ELLIOTT 2,455,984 HYDRAULIC PRESSURE INTENSIFIER UNIT l Filed Jan. 22, 1'945 3 Sheets-Sheet 5 INV-ENTO Gama/y f?. 2f/077 ,QTTORNEY v. 52 vncuun Patented Dec. 14, 1948 4 'STATES PATENT oFF-icc y 2,455,9sigjh`iij..

HYDRAULIC PRESSURE iNTENsmrER-:UNIT 1 G6 dan R. Ellioterernaaxe, Mich., assigner. to

wankee, Wis.

Irving A. Puchner and Edward U.' DenimergvMiL" vAppl,nation January 122, 1945,;serial Nogstsgce? f 9 claims. (c1. sof-'545) This inventionrelates to hydraulic unit for the actuatiunof. Vehicle# .or'truclgfbrakes More particularly the invention relates to thec'ombinatio'n with the hydraulic master .cylinder manually operable..brakes, .ot-.apower unit-'for electing a seconda-ryl powerbrak operation, as shownsimilarly. in .co-.pending ,application Serial No'. v508,033, iiled .October 28, 1943,. new, Patent No. 2,440,654.

" ItJis. the. object. oilthis .invention to. provide in conjunction. with.. the...'conyentonal vhydraulic l master liluid cylinder. governing vehicle braking,y a secondarypW breaking .mechanism including. .'a1,.diaphragm .actuating ,.powerf chamben a hydrauliccylinder.. and a vacuum-airfcontrolling Valve...

v Itis.. the. objectv of.this,.invention.to provide a secondary powerl brakelmechanism characterized by. a manifold `vacuum[suspended? power chamber actuated .y diaphragm, togethrl. with l means .for disconnecting vacuumto. one of ther; sides. thereof and ..a`dmitting air-.. thereto. for.4 actuation and translation.'.tl'iereofn f. Y A

' It.. is .the .further 7 .object herein to.; provision a brake.- operating hydraulic. cylinder .forsupplying to'. .the .vehiclel brakesin-tially .manually operable master. cylinderbrake-.l-uid. under. pressure, andA secondary power. actuated fluid .under pressure.

The invention. relates. to -.tlnevarious arrangement...of elements and .theirl combinations a-s` more fullyset out in connection with .theappended drawings,.ofwl1ich.-.- Y n l Fig'. ,1 isja diagrammaticview showing-.the hydraulic vehiclev .brake ,'actuating-. cylinder, the. manual-.masten .cylinder .brake mechanism,. and the.' .supplementary.` power brake-v-.unit vjoinedthereto.;` n

Fig; 2 isan, .enlarged .elevationalY section of the hydraulic brake). cylinden andvpower brake-unit.

Fig'. 3 is an elevation. viewvfthereoiwith remote power. chamber.. n

y The above. .drawings .are `:merely illustrations of a prefer-able embodimenti'of-:the presentinvention it 'being .understood that other embodiments are,` contemplated within the scopeofthi-s invention as setbutfinA .the appended claims.

` InFifg; 1 "suitablohydrauliclwheel cylinders l are provided adjacent. the vehicle wheel brakes; 2 withhydraulic connections theretobeingsup-v plied throughfconduits yfrom hydraulic cyl- The hydraulic; powerrunit 9 with powerv chamber I!) 'is carriedbybolts l I` secured to the vehicle frame I2y or suitable bracket secured*k thereto. The vacuum hydraulic valve housing.l3 vwith air inlet-s" lll'isjoined tovehicle intake vacuum manio'ld` vI5"by conduit 'i6 and-manifold check valve l'l' for supplying .vacuum fto power chamber `Ill as hreunderexplained.

Referring .to F`g.f2 lthe vehicle brakehydraulic cylinder 4v has an outlet port I8 for communication lwith hydraulic brake lines 3 shown in Fig'. 1. VVK-rile 011.@ Suchfport 'is shown in Fig. 2, Fig.. 1 shows two such outlet ports i8 'for communication with'conduits y' y intake port liaconnects with conduit s from the'` hydraulic master cylinder 1 whereby manually operated brake fluid is supplied under pres,- sure to hydraulic'cylinder 4 tobedirected through the longitl'ldirar'opening2Bi within pi-ston 2| slidingly positioned -incy1inder 4. Piston eXpansion-cup ZZfcarried. by .piston 2l kprovide an effectiv'e hydraulic vs'al within cylinder 4.

Power chamber IU slprovided at one side thereof fwith'a vacuum inlet connection 23 adapted forloonnecti'on yto vacuum conduit i6' yfrom the Vehicle' intake manifold l5. inthe manner illustratedin nigga.' l

The .Vacuun'if valve body housing 24 extending tivi-thin`V power .chamber housing lll is suitably secured Ito' the annular ange 25 of cylinder` housing 4 by bolts 26'and nuts 21. It will be noted thatl said Yflanged portion'25 also forms a part of `airand vacuum Valve body 24. Power chamber In" 'is likewise retained inxed relation to valve ,f body`24 by vbolts-2h' asghcwnv in Fig. 2.

' A hollow aircontrol diaphgram .28 is-periplfier-v allyr'etained between the annularly anged members 24I and 25,-which forinthe control valve body... Hollow diaphragm stiifening plate 29 is secured on ,one side of saidv diaphragm by rivetsv 30,' the' other endsof saidrivets retaining air valve control disc 3|. onthe other side of said diaphragm. .Y n

. 'Disp ,3l lis punched outwardlyto form the annular flanged nembe'r-BZ-which is adapted to unseat aircontrolvdisc533, the latter being norin ally.retained'byI spring-34 over annular air OpeningSSin--airfvalve seat-36; It will benoted secured. between valvel body ange 24 and diaphagm .28'. Y

HollOW li'langedgvalve control piston 31 is reciprocably-.and -slidably `positioned within the end of hydraulic-cylinder 4 in engagement-with spring4 38., the-otherendof which is -seated against As shown in Fig. 2, vacuum is established inY` chamber 44 through openings 45 in hollow power rod 46. It will be noted that. movement to the left of valve control piston 31 causes disc. 41v thereon to sealingly engage plate 29cutting off further vacuum communication to chamber 44.

Initially, the vacuum in chambers 4| vand 44 power diaphragm 48 peripherallysecuredwithinr power chamber i0, assumes the position shown, with return spring 49 being interposed between valve body 24 and diaphragm supporting plate 59. Itjwill be noted that a suitable seal 48""i-s provided'around rod 4S and within .the end of valve housing 24. v

{Said 'diaphragm and plate are Vcentrally secured to hollowpower rod 46 by the opposing nuts'ljand 52 threaded on said rod.

Referring to thecontrol valve body 24 it is seen that air is at alltimes maintained in chamberh53 through A*air `passage 54 formed within Valve bodyfmembers 24and25.- y

As ,valve control pistonv moves to the left relatively torrod 46, in the manner hereafter described, it rst engages diaphragm disc 2S for cutting off furthervacuum `communication between chamber 42 and chamber 44. Further movement to the left of piston 31 causes transla- 'tionV to the leftf'of diaphragm y28 as well as the anged member 32 for unseating spring retained disc k33 from its'seat 36.

" lAir in charr'iber`53` isnow Aable 'to flow through 56, the outer end of which is adju-stably secured by removable cover 51 threadedin the end of hydraulic cylinder 4.

It will be noted that rod 46 is secured at all times to piston 2| by means of the spring retained ball lock 58 so that piston V2| always moves with rod 4B. Ball lock 58 maybe manually disengaged from piston 2| lin the event it is desired to separate said piston and rodffor disc assembly and, or cleaning. Aplug 59 is tightly secured within hollow rod 46 withv a suitable passage formed therein to coincide with and form a part of passage 20am piston 2|. Ball chain 55 interconnects valve 55 and cover 51 to limit movement of said valve.

Y Referring to Figs. `1 and 2,`for conventional operation of the brakes the master cylinder 1 is operated by foot pedal 5 for directing iiuid under pressure through conduit 8,'into port I9 of the hydraulic cylinder, chamber 39 and through passage20 into chamber i'whence it is directed out cylinders l for the vehicle wheels respectively. This initial actuation of break pedal 5 will result in a partial braking eifect upon wheel drums 2 and will also take up the slack of fluid in chamber 55 as well as in conduits 3.

As soon, however, as saidsslack is taken up itwill vbe seenlthat continued and further actuation of brake 4pedal 5 will tend to compress uid within chamber 39 as well as in chamber 6I] with the result that valve control piston 31 is projected to the left. In the i'lrst instance, it will be seen that disc 41 carried by said piston will ,engage the diaphragm disc 29 for closing olf further vacuum communication to chamber 44 forming a part of power chamber I0. It will bef noted that momentarily there is a balanced condition between chambers 4| and 44 with vacuum in both chambers. However, further movement of control piston 31 to the left eiTects movement to the left of diaphragm 28 as Well asthe flanged member y32 which unseats spring retained air'control disc'33.

Air which is'const'antly in chamber 53 is thus free to rushthrofugh opening 35 in'valve seat 36 for"y communication' with chamber 44 'through hollow.v rod 46.' yInstantly there is a forceful translation'of diaphragm 48 to the right due to the pressure differential between chambers4 4| and 44 which is proportionate to the surface area of said diaphragm, andwhich results in forceful translation of power rodf4'6. Hydraulic piston 2| eingl joined thereto istalsotranslated forcefully to the'right, first sealing off passagev 2|] by engagement of valve member 55.v Further movement vof hydraulicl pistonv2| tends to exert a compressive force jupon( the iiuid in chamber 60 with the result that a secondary power braking is effected'through lines 3. It will be understood that as'soon as passage 2|) is closed off by engagement with v'alve'member 55 uid under pressure, which is maintained by continued application of brake pedal 5, is directed to chamber 39; and inasmuch as 'passage 20 is now closed, it will be seen that a degree ofk iiuid pressure eiis'tsfor cooperative action upon the end of piston *2| working in unison with the power rod 46 which is also effecting la pressure movement on piston 2|' relativef'to the hydraulic fluid in chamber 6D. f Y.

For example, while 'the' initial braking pressure may be approximately 200 pounds per square inch, power chamber I9 effects a substantial multiplication of braking Vpressure so that approximately`800 to'1000`pounds per square inch pressure is available. VIt is understood that the above pressure-sI are givenlrnerely by way of illustration and naturally would be varied depending upon 'the size of power chamber lll and the surface area of diaphragm 48. Movement 0I piston 2| to the rightwincreasing the volume of chamber 39 partially r'educesthe existing iiuid pressure therein permitting a partial return of valve 'pisto`n31' to"1 `the right under action of coiled spring 38.v `Diaphragm 28 and plate 29, under action offspring 34, follow Valve piston 31l to the right,'permitting air disc 33 to seat itself under" action of `said spring, 34, cutting off further air communication between chambers 53 and 44. Said, valve assembly is now in a balanced condition with further air and Vacuum communication tochamber 44 effectively cut off.

Brake release is effected by relieving the manual pressure from master cylinder Y' l with the result-thatthe pressure in chamber 39' is reduced permitting control -pisto'n 31"..tdreturntlto. its initialnositiom'under'action of coil sprng.- As'son as control? piston 31-reaches the position shown' in Eig?. 2,lvacuux'n. communication is'again established 'between chamber 4 If and" chamber 44,v witn'the'result tnotan equilibrium in pressure is! 'established on opposite sides of diaphragm 48. Said 'diaphragm :then returns to .its initial position shown in Fig. 2lunder action ofcoil spring-` 491-11? will-be noted! that V,return ot diaphragm` 48`-toitsf initial' position` also eiects a correspondingdetirn of- Apower rod 46 a`s Wellas hydraulic motionl 2li' secured thereto.

stop` member 61 is threaded through hydraulic cylinder 4 Aand. projectsinto* clfiamber` 39 "to provide alimitat'ion nfth'eieturn movement of piston 2li aswell ast'n'ower-'rod '46 and diaphragm 48:'sered thereto'f." The Areturn of pist0n`2l to its"ir 1itial position reslts in lthe unseating ofv valve'member SS-again'opening passage 20 Vin saiiif` piston 'which communicates' with chamber 39-""Thus all operatingu members are again'in their initial positionsr'eady forthe negt actuation ofthe brakes. y' i y that in the event of a faili'ire'of' the 'power brakinhgsystem or the air and;v vacuum control valve therein mantieni/'ap p li tio'nf'ofthebrakes'is'still available as above Afterfaplication ofV the'power brakes, and on release of foot'edall; thfe'ffi'idp'ressurein contr'ol'chamber 39" is reduced approaching zero', permit'tirigl ,vali/e" control piston'4 3l' to 'gradually return A"tofvthelrigljiterelativelyfto power rod 46, until: it 'reaches 4"its initial position shown in Fig. 2, At the same time, withv pressure .in onainbjet et- `anzi'opnirig 'zonstiufoiosed piston zl's'talts movingebaol' 'to the 'initial position shown Iin,lig`. `2 dueto the diiferentialof pressure QIQOPP'OS?? S'devthreQL l Y The. etiiin movementof piston .2| isilimited' by. this feiern'. movement 0f.. power, rod. 46, and 'tagnilfio which .itis joined.' AS@ Short pe`...d of ,time elansesbiorfe full vacuum is again.' sieblslldin chamber. 44.,.dephrag1i igtdsito lag" irl/returning tolits inoperative position,k as' shown in Figl`V 2,eve'n 'though under vexpansive actioni'fof spi1g 4$, This. lag` .would be transmittedtoV pis/t'onl'ldelayin'g its return,v for efiectingwcompletebrake release.

However, .it is seen'b'y the initialupressure differential between chambers '39 andv 60 that, on releasleofh pedal 5,',niston 21 is assisted in its return; nugtnerniofef bau chaines-5y;- iimits the returnY movement of valve 55j guaranteeing the quifclopenin'g of lpassagelliof piston 2l.'L 4Opening` of nassag'e `2'() immediately effects 'complete brake releaser` with yiiuid under pressure in chamberGil f 'rec to escape. Thus brakev release isf'loroiiiit whichi's a'great advantage'over power brakes of differenty construction wherein means are not provided 'for assistingvin thebrake release function.

lower chamber I U isy advantageously secured o r formed integrally with controlvalve 24-25 to providea compact unit which maybe positionedanywhere on Athevehicle orr truck frame. VI-low-4 ever,` it iscontemplatedthat said powerV chamber c'old be remote'from the control *Valve with a suitablelinkage' interconnecting the diaphragm aridtlie valve actuating power rod 46;

O'i` the other handit is also'contemplated that valve actuating" rod 4lioouldbe forcefullyactuat'ed' by any' other suitable power.. source acting yit 'will' be understood Itlwillbe understoodithat while the powert chamber lo is shown in Fig. 2y with: a' flexible movable. diaphragm therein, it Ais contemilat'ed that saiddpower 'chamber could be constructed withta recip'rocable piston-therein. Creationlot pressure. differentials von opposite sides of the *pis*-l ton would, .be effectecliexactly as `described with respect ytolFigy2.-

Fig...3 shows the combination .of hydraulic brake c5i1inderi4; withtiuid.deliveryl outlet I8,and air and .vacuumvcontrol valve Z4- 25o However, the

y assliownfin Fig.i2, with power 'shaft 46".;recipro-r cably... positioned therethrough effecting move-v ments ot the: fluid control piston 2li. Connecting .roddirprojects from piston Mire- ;ciprocably. provisioned within powerchambercylinder 63.. Rod 64 isfpivotallyvjo'inedatits end 65 ,toleverSS centrallypivotedat 61 to bracket 68-l or. other. member` forming` a 'part of the vehicle frame... t 'I' Power. shaft 45 is pivotally and looselyv joined at ill to the other end` of lever 'B6-.fA YVacuum.chamber .ll iin" cylinder 63 4is joined. tothevehicle enginefintak'e manifold lby com duit l2 :as .shown diagrammatic'ally in 4yrlig. `'3.- Conduit i2:Yalsoprovides vacuum communication' to the valve vacuum passage 43 shown in detail in. Fig. z.4 operating chamber is on the oth'r'ide of piston E2 is supplied airor vacuum fron'i'the control valve outlet 'M- through conduitly v It is understood that Valve outlet i4 communi-` cates with the interior charn'ber'lii-of` valve ill-viii",-v and is provided air kfrom intake portV i4 and, orn vacuurnvfrom port 43jdependinng'unon the'r'osi.i tioning of the inoi'ablevaivein'enibei withnsid valve housingnvheretoiore describedin ,detavi'lQ l Having described my r'inventions,reference shouldbe had towtheclaims which follows forA determiningnthe scopefthereof, Y

I dan..

1 Tine combination, a; hydraulic. cyiinden. a valve control. pistonand' a fl'uidx'lcontrol piston with an lopening therethrough onpositely disposed; therein providingA a, uidchamber. therebetween, there .being a l.secondary fluid chamber in said cylinder .i or .delivering. fluid under pressure.A manually `vcontrolled pressure fluid sourcejoining Said rstuchamben adapted, forcom 1nunication with saidsecondary chamber. throgh said huid; control piston, .and forop'erative pressure engage-A I Illlii..A With .said valve control piston for eiectingx movement thereof, a power chamber, a rriovabley member. therein, means on, said men'iberA slidably extending through said valve` control piston andA joined at itsl outer endv to said fluid control piston anud-adaptedtoforcefulftranslation upon a pressure differential on opposite sides of said movable chamber,.anair and vacuum control valveintermediatesaid. cylinder and power chamber engageableloy said valve control piston for effectingsaid diierential, valve means in said secondary-fluidJ chamber-forclosin'g the opening in said iiuid controlpiston on movement thereof in one direction, and` flexible limiting means joined to said valve means'for'unseatinghthe isame relative to said` member therein, means on said member slidably extending through said valvefcontrol piston and joined atits outer end to said fluid control piston and adapted to foreceful translation upon a pressure differential on opposite sides of said movable member, an air and vacuum control valve intermediate `said cylinder and power chamber engageable by said valve control piston for effecting said differential, resiliently urged valvemeans in said cylinder for closing communication through said fluid control piston on movement thereof in vone direction, and flexible limiting means joined to said valve means for unseating the same relative to said piston opening on movement thereof in the opposite direction.

`3. The combination, a hydraulic cylinder, air and vacuum valve control and brake fluid control pistons therein, the latter pistonhaving an opening therethrough, a manually controlled pressure fluid source intermediate said pistons adapted for'communication through said fluid control piston and for operativel pressure engagement withsaid valve control piston, a power chamber, a movable member therein, means on said member slidably extending through said valve control piston and joined at its outer end to said fluid control piston and adapted for forceful translation upon a pressure differential on opposite sides of said movable member, a vacuum source joining said power chamber on one side of said movable member, an air and vacuum control valve intermediate said cylinder and power chamber for normally maintaining vacuum communication to the other side of said movable member, but adapted on movement of said valve control piston engaging said valve for cutting off said latter vacuum communication and establishing air communication thereto, resiliently urged valve means in said cylinder for closing communication through said fluid control piston on movement thereof in one direction, and flexible limiting means joined to said valve means for unseating the same relative to said piston opening on movement thereof inthe opposite direction.

4. The combination, a hydraulic cylinder, a power chamber containing a movable diaphragm centrally therein defining a vacuum chamber and an operating chamber on opposite sides thereof, an air and vacuum control valve intermediate and co-axial with said cylinder and power chamber adapted to alternately provide air and Vacuum communication to said operating chamber, a vacuum source communicating with said vacuum chamber, a valve operating piston adapted to engage said valve and a brake uid control piston having'an opening therethrough in said cylinder, a manuallycontrolled pressure fluid source intermediate said pistons adapted for communication through said fluid control piston and for pressure engagement with said valve operating piston, a plunger rod slidably provisioned through said valve and valve operating piston joined at one end to said diaphragm and at its other end to said fluid control piston, resiliently'urged means in vsaid cylinder for closing communication through said fluid `control piston Aon movement thereof in one direction, and ,flexible limiting means joined to saidI valve means for unseating the samerelative to said piston opening on movement thereof in the opposite direction.

5. The combination,` a hydraulic cylinder, a power chamber ,containing a movable diaphragm therein vdefining a vacuum chamber and an operatingA chamber on lopposite sides thereof, an air and vacuum control valve housing intermediate and CD-axialwith said cylinder and power chamber,` amovablevalve member therein, a diaphragm peripherallysecured within said housingand,supportinggsaid valve member, the latter being adaptedto alternately provide vacuum and air kcc,mmunication through said` housing to said operating chamber, avacuum source communieating with said vacuum chamber, a valve operating .piston adapted to operatively engage said movable valve member, and a iluid control piston having Lan opening., therethrough both in said cylinder, a manually controlled pressuregfluid source intermediatesaid pistons adapted for com-- munication through said fluid control piston and for pressure engagement with said valve operating piston, a plunger rod slidably provisioned through said housing, movable valve member, and valve piston,joined` atione Aend to said rst diaphragm and at its other end to said fluid control piston, resiliently urged valve means in said cylinder for closing communication through said fluid control piston on movement thereof in one direction,. .and flexible limiting means joined to said valve means for unseating the same relative to said .piston opening on movement thereof in the opposite'direction. Y

. 6. The combination, a hydraulic cylinder, a fluid control piston having an opening therethrough and a valve control piston in said cylinder in spaced relation, a manually operable pressure uid source 4.between said pistons adapted for communication through said piston opening, and for operative pressure engagement with the other piston, a power chamber, a movable memr. ber therein adapted to translation upon a pressure differential on opposite sides thereof, a longitudinally movable plunger rod joining said movable member'at one end and said fluid control piston at its other end and slidably disposed through said valve control piston, an air and vacuum control valve co-axial with and `intermediate said cylinder and'power chamber engageable by said valve control piston for effecting said differential, resilient valve means in said cylinder for closing the opening in said fluid control piston on movement thereof in'one direction, flexible limitingmeans joined to said valve means for unseat-ing the same .relative to said piston opening on movement thereof in theopposite direction, resiliently .urged means intermediate said valve control pistonA and the end of said cylinder.

7. The combination, a hydraulic cylinder, valve control and uid control pistons oppositely disposed therein providing a fluid chamber therebetween, said fluid control piston having an opening therethrough there being a secondary fluid chamber in said cylinder for delivering fluid under pressure, a manually `controlled pressure uid source joining said rst chamber, adapted for communication with said secondary chamber through said fluid control piston, and for operative pressure engagement with said valve control piston for effecting movement thereof, a power chamber, a movable membertherein, means on said member slidably extending through said e valve control piston and joined to said fluid control piston and adapted to forceful translation upon a pressure differential on opposite sides of said movable member, an air and vacuum control valve intermediate said cylinder and movable member engageable by said valve control piston for effecting said differential, resiliently urged valve means in said secondary chamber for closing communication through said iiuid control piston on movement thereof in one direction, and exible limiting means joined to said valve means for unseating the same relative to said piston opening on movement thereof in the opposite direction.

8. The combination, a power chamber having a movable member therein defining an operating chamber and a vacuum chamber, a hydraulic cylinder containing a brake fluid control piston and a valve control piston, a manually controlled pressure fluid source intermediate said pistons.

adapted for communication through said uid control piston and for operative pressure engagement with said valve control piston, a valve hous- ,ing having air and vacuum inlet ports, and an outlet port communicating with said operating chamber, a hollow reciprocable valve member in said housing, a diaphragm peripherally secured to said housing and centrally carrying said movable member providing a normally closed air passage between said air port and said outlet port, said valve control piston being normally spaced from said valve member providing a normally open vacuum passage between said vacuum port and said outlet port, whereby progressive movement in one direction of said valve control piston closes said vacuum passage and further movement thereof causes movement of said valve member to open said air passage, and partial movement of said valve piston inthe opposite direction permits closing of said air passage, and further movement in the same direction opens said vacuum passage, whereby vacuum and air communication are -alternately provided to said operating chamber, a Vacuum source communieating with said vacuum chamber and with said vacuum inlet port, and a plunger rod secured to said power chamber movable member at one end 10 and to said fluid control piston at its other end, slidably provisioned through said valve housing, said valve member, and through said valve operating piston.

9. A power unit comprising a hydraulic cylinder containing uid to be supplied under varying pressures to the wheel brake cylinders of a vehicle, a piston with an opening therewith in said cylinder operable on said fluid, a manually operable pressure fluid source communicating with said ud, a power chamber, a movable member therein, means on said movable member joined at its outer end to said piston and adapted to translation upon a pressure dierential on opposite sides of said movable member, an air and vacuum control valve co-axial with and intermediate said cylinder' and power chamber for effecting said diierential, a secondary piston in said hydraulic cylinder in spaced relation to said rst piston y engageable with said valve and operable upon by said manually operable pressure fluid source for controlling said valve, valve means in said cylinder for closing the opening in said rst piston on movement thereof in one direction, and flexible limiting means joined to Said valve means for unseating the same relative to said piston opening on movement thereof in the opposite direction.

GORDON R. ELLIOTT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Rockwell Mar. 20,